Leakage containment system for run-away subsea wells

ABSTRACT

A device comprising a sleeve in the form of a cylinder to be placed over a defective deep-water subsea oil-well equipment structure such as a defective Blow-Out Preventor (BOP), said cylinder being anchored by suction anchors and including a roof in the form of a funnel and including pipelines for introducing methanol for preventing hydrates formation and pipelines for removing water/oil/methanol mixture, where the space between the inner wall of the cylinder and the outer surface of the sub-sea equipment may be filled with grout, is suitable for stopping run-away oil-well leakage. A process for stopping run-away oil-well leakage by using said structure is also disclosed.

The present invention concerns an assembly forming a containment system for run-away subsea wells. Said system comprises a sleeve with dimensions larger than the relevant Blow-Out Preventer (BOP) device of the oil-well topped by a frustrum roof forming a funnel above the BOP, said roof being equipped with an exhaust chimney with a closure valve including a connection device for anchoring sealing and/or anchoring equipment to said exhaust chimney, the assembly further comprising a number of suction anchor pods disposed at the periphery of the sleeve, said sleeve also including an injection inlet for grout at its base and said roof including at least one injection inlet for methanol and at least one outlet oil/water/methanol mixture. The sleeve may in a preferred embodiment include a level gauge for monitoring the level of injected grout.

One of the problems to be solved with the present invention is to provide a containment system for run-away oil wells in deep-sea drilling. An offshore exploration well especially in deep-water and/or under HP/HT conditions (up to 1200 bars pressure and 200° C. temperature) is mandatorily equipped with a blow-out preventer (BOP) which shuts down the well automatically when abnormal pressure is encountered in order to stop the uncontrolled gushing of fluids. No independent barrier exists otherwise if the BOP cannot operate due to the failure of one of its components. Mitigating the oil leakage is complicated further by the formation of hydrates at such depths as water mixes with methane, said hydrates clogging up export lines which convey the oil/water mixture in potential rescue devices.

Examples of BOPs according to the prior art include the device disclosed in U.S. Pat. No. 4,416,565 A comprising a cylinder with a funnel-shaped roof being constructed as a chimney with a valve to be placed over a well with an uncontrolled blow-out. The cylinder has an exit leading oil and gas to the surface.

Also in U.S. Pat. No. 4,318,442 A is there shown a cylinder with a chimney being placed over a well with an uncontrolled blow-out and with an exit for oil and gas from the well.

From US patent application 2006/0225810 there is disclosed a sarcophagus being lowered onto a wreck on the seabed for emptying the wreck for oil and gas. The sarcophagus is anchored to the seabed by the aid of suction anchors and it is injected methanol into the sarcophagus for preventing the formation of hydrates when the wreck is emptied.

The blow-out rescue device according to the present invention is disclosed infra under reference to the enclosed FIGURE.

The containment system according to the present invention comprises the following elements:

1. a container lowered over the faulty BOP comprising

-   -   a sleeve (preferably cylindrical) (item 1A), in one embodiment         approximately 4 m in diameter and 12 m high (the dimensions         being adjusted to the relevant BOP over which the sleeve is to         fit, specified by the supplier of the BOP);     -   a frustrum roof (item 1B) the slope of which will depend on the         internal friction of the hydrate crystals (normally between 30         and 60°);     -   an exhaust chimney (item 1C) (in one embodiment with a diameter         of up to 36″) equipped with a closure valve and crowned by a         flange, which can be used as a base for anchoring and sealing         equipment or pipe landed at the top of the chimney in the event         of unforeseen intervention.

2. at least three suction anchor pods (item 2) disposed at the periphery of the main sleeve (cylinder). The suction anchor pods may in one embodiment have a diameter of about 1.5 m and will include penetration marks and pressure control valves.

3. a grouting system comprising manifolded injection lines (item 3A) at the base of the sleeve and a level gauge (item 3B) at the top of the sleeve.

4. a methanol injection system comprising small bore branched pipes (item 4A) piercing the conical roof of the sleeve and preferably associated with a gauge (4B) which measures the relative concentration of seawater and methanol in the oily mixture trapped under the roof.

5. one or more outlets (item 5) at the base of the chimney each activated by a closure valve and connected to an export riser conveying the oily mixture to the sea surface. While one outlet only should normally be open at any time, the other inactive outlets would enhance the redundancy of the export system in the event of the active line becoming clogged. Furthermore, using a different diameter for each outlet line, e.g. from a diameter of 6″ to a diameter of 12″, would allow adapting to variations in the debit of the uncontrolled well and hence optimize the flow in the riser throughout the duration of the operation. The number of outlet/export lines (item 5) could be 2, 3 or 4, possibly more, each optionally characterized by a specific diameter different from each other. Using several outlet lines would also make the containment system according to the present invention more versatile. In the event that the outlet line in use is clogging up through the (unforeseen) formation of hydrates or an unexpected production of sand, it may then be possible to open up a second outlet line and simultaneously reverse the flow direction in the clogged-up line by flushing or purging this line with methanol, thus dissolving the hydrates and clearing the previously clogged-up outlet/export line again. This procedure will ensure continuous export of fluids through the outlet/export lines and avoid pressure build-up under the hood/funnel/roof of the device according to the invention.

The material of the parts of the device/system according to the present invention is to be metal or a metal alloy withstanding the conditions of pressure and temperature existing at the oil-well in question. Also the metal or metal alloy should be non-corrosive (at least for a period of time relevant for making the oil-well safe). The metal of choice is steel, tempered steel or stainless steel.

The present invention also includes a process for stopping the oil and gas outflow from a run-away oil-well (uncontrolled blow-out). The process for stopping such outflow includes the following steps:

1. The container/sleeve is lowered over the BOP with the main chimney valve open to allow free exhaust of the oil and gas bursting from the top of the (damaged) BOP. Methanol may be injected through line (4) at this early stage to prevent hydrate formation and clogging of the chimney.

2. The valves of the suction pods (2) are activated in order to create a hydrostatic depression sufficient to drive the main container (1) deep into the sea bottom, and hence achieve adequate sealing at its base.

3. Grout is then injected at the base of the container/sleeve to fill its annulus (space between the BOP and the internal surface of the sleeve) including the BOP and ensure a good bonding of the two objects. Raising of the grout in the annulus is monitored until the free-surface of the grout reaches approximately the top of the sleeve at its intersection with the conical roof. Throughout this phase, the chimney remains open and continues to allow free passage of the fluid bursting from the BOP and also of the seawater trapped inside the container/sleeve and displaced by the grout.

4. After grouting is complete, the remaining volume of trapped seawater more or less corresponds to the volume of the conical roof. This seawater is mixed with oil and gas from the well and with methanol which continues to be injected.

5. As more methanol is injected, its concentration in the mixture increases while that of seawater decreases until the critical threshold of hydrate formation is reached. The chimney valve is then progressively closed as the riser export line (5) opens, which then conveys a mixture consisting almost exclusively of oil, gas and methanol, no longer prone to hydrate formation. 

1. An assembly forming a containment system for run-away oil-wells comprising: a sleeve with dimensions larger than a BOP device of an oil-well forming a frustrum between the sleeve and the BOP, said sleeve including a roof forming a funnel above the BOP, said roof being equipped with an exhaust chimney with a closure valve including an interface for anchoring and sealing equipment to said exhaust chimney, the assembly further comprising a number of suction anchor pods disposed at the sleeve's periphery, said sleeve also including an injection inlet for grout at its base and said roof including at least one inlet for methanol injection and at least one outlet for export of oil/water/methanol mixture.
 2. The assembly according to claim 1, wherein the sleeve includes a level gauge for monitoring a level of injected grout.
 3. A process for shutting down a run-away oil-well with a damaged BOP, said process comprising the steps of: lowering the container/sleeve of the assembly according to claim 1 is over the BOP with the main chimney valve open to allow free exhaust of the oil and gas bursting from the top of the BOP, wherein methanol may be injected through line (4) to prevent hydrate formation and clogging of the chimney; activating the valves of the suction pods (2) to create a hydrostatic depression sufficient to drive a main container (1) deep into the sea bottom, and hence achieve adequate sealing at its base; injecting grout at the base of the container/sleeve to fill its annulus which is the space between the BOP and the internal wall of the sleeve including the BOP and ensure a good bonding of the two objects wherein raising of the grouting in the annulus is monitored until the free-surface of the grout reaches the start of the conical roof, and throughout this phase, the chimney remains open and continues to allow unimpeded exhaust of the fluid gushing from the BOP and also of the seawater trapped inside the container/sleeve and displaced by the grout, until grouting is complete; mixing the remaining volume of trapped seawater with oil and gas from the well and with the injected methanol so as to substantially correspond the volume of seawater to the volume of the conical roof; injecting methanol so that its concentration in the mixture increases while that of seawater decreases until the critical threshold of hydrate formation is reached; and progressively closing the chimney valve as the riser export line (5) opens to convey a mixture consisting almost exclusively of oil, gas and methanol, no longer prone to hydrate formation.
 4. A process for shutting down a run-away oil-well with a damaged BOP, said process comprising the steps of: lowering the container/sleeve of the assembly according to claim 2 over the BOP with the main chimney valve open to allow free exhaust of the oil and gas bursting from the top of the damaged BOP, wherein methanol may be injected through line (4) to prevent hydrate formation and clogging of the chimney; activating the valves of the suction pods (2) to create a hydrostatic depression sufficient to drive the main container (1) deep into the sea bottom, and hence achieve adequate sealing at its base; injecting grout at the base of the container/sleeve to fill its annulus which is the space between the BOP and the internal wall of the sleeve including the BOP and ensure a good bonding of the two objects wherein raising of the grouting in the annulus is monitored until the free-surface of the grout reaches the start of the conical roof, and throughout this phase, the chimney remains open and continues to allow unimpeded exhaust of the fluid gushing from the BOP and also of the seawater trapped inside the container/sleeve and displaced by the grout, until grouting is complete; after grouting is complete, mixing the remaining volume of trapped seawater with oil and gas from the well and with the injected methanol, so as to substantially correspond the volume of seawater to the volume of the conical roof; injecting methanol so that its concentration in the mixture increases while that of seawater decreases until the critical threshold of hydrate formation is reached; and progressively closing the chimney valve as the riser export line (5) opens to convey a mixture consisting almost exclusively of oil, gas and methanol, no longer prone to hydrate formation. 